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United States Patent |
5,723,639
|
Datta
,   et al.
|
March 3, 1998
|
Esterification of fermentation-derived acids via pervaporation
Abstract
A low temperature method for esterifying ammonium- and amine-containing
salts is provided whereby the salt is reacted with an alcohol in the
presence of heat and a catalyst and then subjected to a dehydration and
deamination process using pervaporation.
The invention also provides for a method for producing esters of
fermentation derived, organic acid salt comprising first cleaving the salt
into its cationic part and anionic part, mixing the anionic part with an
alcohol to create a mixture; heating the mixture in the presence of a
catalyst to create an ester; dehydrating the now heated mixture; and
separating the ester from the now-dehydrated mixture.
Inventors:
|
Datta; Rathin (Chicago, IL);
Tsai; Shih-Perng (Naperville, IL)
|
Assignee:
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University of Chicago (Chicago, IL)
|
Appl. No.:
|
543522 |
Filed:
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October 16, 1995 |
Current U.S. Class: |
554/154; 210/638; 210/640; 210/649; 210/650; 210/651; 554/167; 554/170; 560/231; 560/234 |
Intern'l Class: |
C07C 051/00 |
Field of Search: |
554/167,154,170
560/231,234
210/638,640,649,650,651
|
References Cited
U.S. Patent Documents
2956070 | Oct., 1960 | Jennings et al.
| |
Other References
E.M. Filachione et al., Lactic Esters by Reaction of Ammonium Lactate with
Alcohols, Sep. 1952, pp. 2189-2191, Industrial and Engineering Chemistry,
vol. 44.
|
Primary Examiner: Dees; Jose G.
Assistant Examiner: Carr; Deborah D.
Attorney, Agent or Firm: Cherskov & Flaynik
Goverment Interests
CONTRACTUAL ORIGIN OF INVENTION
The U.S. Government has rights in this invention pursuant to Contract No.
W-31-109-ENG-38 between the U.S. Department of Energy and the University
of Chicago representing Argonne National Laboratory.
Claims
The embodiment of the invention in which an exclusive property or privilege
is claimed is defined as follows:
1. A method for esterifying ammonium carboxylate salt comprising:
a.) mixing the salt with an alcohol to create a mixture;
b.) heating the mixture in the presence of a catalyst; and
c.) subjecting the mixture to a pervaporation process.
2. The method as recited in claim 1 wherein the ammonium carboxylate salt
is an ammonium salt of an organic acid selected from the group consisting
of lactic acid, propionic acid, butyric acid, acetic acid, succinic acid
and combinations thereof.
3. The method as recited in claim 1 wherein the alcohol is mixed with the
ammonium carboxylate salt in a mole ratio of between approximately 1:1 to
6:1.
4. The method as recited in claim 1 wherein the alcohol is selected from
the group consisting of methanol, ethanol, propanol, isopropanol, butanol
and combinations thereof.
5. The method as recited in claim 1 wherein the mixture is heated to a
temperature selected from a range of between approximately 75.degree. C.
and 150.degree. C.
6. The method as recited in claim 1 wherein the step of subjecting the
mixture to a pervaporation process consists of contacting the mixture to a
pervaporation membrane selective to ammonia and water so as to remove
water and ammonia from the mixture to create a retentate fraction.
7. The method as recited in claim 6 wherein the retentate fraction is
subjected to a pervaporation membrane selective to ester so as to remove
ester from the retentate fraction.
8. The method as recited in claim 6 wherein the retentate fraction is
subjected to distillation so as to remove ester from the retentate
fraction.
9. A method for esterifying a salt of a fermentation derived carboxylic
acid comprising:
a.) splitting the salt into its cationic and anionic part;
b.) mixing the anionic part with an alcohol to create a mixture;
c.) heating the mixture in the presence of a catalyst to create an ester;
d.) dehydrating the now heated mixture by contacting the mixture to a
pervaporation membrane selective to water so as to remove water from the
mixture; and
e.) separating the ester from the now-dehydrated mixture.
10. The method as recited in claim 9 wherein the step of splitting the salt
into its cationic and anionic parts consists of subjecting the salt to
mineral acid.
11. The method as recited in claim 10 wherein the mineral acid is present
in equimolar quantities to the anionic part.
12. The method as recited in claim 9 wherein the organic acid is selected
from the group consisting of lactic acid, butyric acid, succinic acid,
acetic acid, propionic acid and combinations thereof.
13. The method as recited in claim 9 wherein the alcohol is selected from
the group consisting of methanol, ethanol, propanol, isopropanol, butanol
and combinations thereof.
14. The method as recited in claim 9 wherein the alcohol is mixed with the
anionic part in a molar ratio selected from between 1:1 to 6:1.
15. The method as recited in claim 9 wherein the mixture is heated to a
temperature selected from a range of between approximately 75.degree. C.
to 150.degree. C.
16. The method as recited in claim 9 wherein the step of removing the ester
from the now-dehydrated mixture consists of distilling the ester from the
mixture.
17. The method as recited in claim 9 wherein the step of removing ester
from the now-dehydrated mixture consists of subjecting the now-dehydrated
mixture to a pervaporation membrane selective to ester.
18. A method for esterifying amine carboxylate salt comprising:
a.) mixing the salt with an alcohol to create a mixture;
b.) heating the mixture in the presence of a catalyst; and
c.) subjecting the mixture to a pervaporation process.
19. The method as recited in claim 18 wherein the alcohol is mixed with the
amine carboxylate salt in a mole ratio of between approximately 1:1 to
6:1.
20. The method as recited in claim 18 wherein the alcohol contains from one
to four carbons.
21. The method as recited in claim 18 wherein the mixture is heated to a
temperature selected from a range of between approximately 75.degree. C.
and 150.degree. C.
22. The method as recited in claim 18 wherein the step of subjecting the
mixture to a pervaporation process consists of contacting the mixture to a
pervaporation membrane selective to volatile amines so as to remove
volatile amines and water from the mixture to create a retentate fraction.
23. The method as recited in claim 22 wherein the retentate fraction is
subjected to a pervaporation membrane selective to ester so as to remove
ester from the retentate fraction.
24. The method as recited in claim 22 wherein the retentate fraction is
subjected to distillation so as to remove ester from the retentate
fraction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the esterification of organic
acids, and more particularly, this invention relates to a method for a
process for making high purity esters from fermentation derived organic
acids using pervaporation processes.
2. Background of the Invention
Organic acids and esters of organic acids offer great feedstock potential
for polymer and specialty product manufacture. Esters of organic acids
are, by themselves, very valuable products, particularly as
environmentally benign, non-toxic, non-halogenated solvents.
Demand for such "green" solvents continues to increase. For example,
lactate esters such as ethyl lactate and butyl lactate have solvating
properties similar to the more toxic ethylene glycol ethers. Lactate
esters also can replace halogenated solvents, serve as intermediates for
polymer production, and be converted to polymers by condensation. In as
much as these acids and their corresponding esters are used as solvents,
chemical or polymer feedstocks, and flavor and fragrance ingredients, they
must be highly pure.
Fermentation-derived acids are always accompanied by some residual
impurities such as simple sugars, carbohydrates, proteins, amino acids,
and other organic and inorganic compounds. For example, a high-yield,
crude fermentation broth engineered to produce lactic acid contains not
only 80-90 grams per liter (g/l) lactate but also 10-20 g/l of
contaminating (unfermented) carbohydrates, proteins, cell parts and other
organics. These residual impurities usually have to be removed to attain
the highly-pure products, as discussed supra, before their use as
specialty chemicals.
Organic acids such as lactic, butyric, succinic, acetic and propionic acids
are produced by fermentation of carbohydrates with anaerobic bacteria.
Generally, the acids appear as ammonium-, sodium-, calcium-, and
potassium-salts, with the cations initially introduced into the
fermentation liquor as hydroxides or carbonates to maintain an optimal,
near neutral pH for the bacteria. The salts are then converted to their
respective acids by acidification with mineral acids, such as sulfuric,
with production of the byproduct salt such as sodium, calcium or ammonium
sulfate. However, the organic acids produced by this process are not
suitable for certain polymerization processes or as chemical feedstocks.
Employing recently developed water-splitting electrodialysis procedures can
eliminate the by-product salt and the corresponding alkali can be recycled
to fermentation. However, the use of water-splitting processes requires an
additional step.
A method to further purify the organic acids is through esterification
whereby volatile alcohols such as methanol, ethanol or butanol are used to
convert the desired organic acid to its ester, with the ester subsequently
separated from the reaction liquor via distillation.
Drawbacks to using volatile alcohols in typical high temperature
esterification processes are numerous. First, alcohols, with their lower
boiling points compared to esters, vaporize without reacting efficiently
with the acid. Large molar excesses of alcohol therefore have to be used,
vaporized, and re-condensed, all of which leads to increased costs and
energy use.
The use of volatile alcohols also leads to the formation of azeotropes,
some of which are low boiling. These compounds have to be broken down by
further solvent-distillation to remove the water and make the ester.
Also inherent with high temperature esterification procedures is the
formation of undesirable products. For example, in the presence of the
esterification catalyst (typically acidic), the impurities in the crude
acid form large amounts of thermal- and acid-catalyzed breakdown
contaminants. Some of the impurities are derived from the residual
carbohydrates which under acid catalyzed conditions produce aldehydes.
These aldehydes interfere with subsequent chemical conversion or
polymerization reactions, and many have undesirable odor. Other impurities
are derived from the residual carbohydrates and proteins which can react
to make colored residues or tars or Malllard reaction byproducts.
As a result of the above-identified problems associated with volatile
alcohol use in esterification processes, the costs of final product are
large. For example, the step of making methyl lactate from lactic acid
increases costs by $0.10 per pound, and requires 5-6 pounds of steam.
Therefore, traditional esterification processes currently are not
economically viable if fermentation-derived organic acids are used as
polymer or chemical feedstocks, compared to petrochemical feedstock
sources.
One of the main technical problems of making an ester is the removal of
water from the reaction mixture without removing the alcohol, and thus
driving the reaction, depicted in Equation 1, below, to the right where
R--COOH is the carboxylic acid, R'--OH is the alcohol, and RCO.sub.2 R' is
the ester.
##STR1##
The challenge for esterification of ammonium and amine-based salts, such as
ammonium carboxylate is the removal of ammonia and water, as they are
formed, but without removing the alcohol, thus driving the reaction,
depicted as Equation 2, to the right.
##STR2##
As first disclosed in E. M. Filachione, et al. Industrial and Engineering
Chemistry, 44, 2189-2190, typical processes for producing esters from
ammonium carboxylates require high temperatures, up to 200.degree. C. In
these high temperature processes, only higher boiling alcohols such as
butanol or longer chain alcohols are usable so as to minimize alcohol
volatilization. Also, large excesses of the alcohol are necessary.
Furthermore, the process produces reaction by-products that are not
esters. As such, typical esterification procedures of ammonium
carboxylates also can prove costly, and still do not provide highly pure
esters.
A need exists in the art to provide a more efficient method of
esterification of fermentation-derived organic acids. The method should
employ fewer production steps, use less energy, use lower boiling
alcohols, and provide purer yields of esters. The esters subsequently can
be used as solvents or for chemical and polymer feedstocks.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for
esterification of organic acids that overcomes many of the disadvantages
of the prior art.
Another object of the present invention is to provide a method for
production of organic acids which will yield high grade product for use as
chemicals or feedstocks. A feature of the invention is the incorporation
of pervaporation in the esterification process of the organic acid
purification procedure and a lowering of reaction temperatures. An
advantage of the invention is the elimination of the need for large
amounts of volatile alcohols and therefore a lowering of costs associated
with esterification procedures.
Yet another object of the present invention is to provide an improved
method for production of high grade esters from fermentation-derived
ammonium carboxylates. A feature of the method is the direct conversion of
the ammonium carboxylates to the ester, without first converting to its
respective acid. An advantage of the method is the elimination of the use
of a salt-cleaving step, such as the addition of mineral acid, thereby
conferring cost savings and eliminating waste salt byproduct.
Briefly, the above objects and advantages of the present invention are
achieved by a method for esterifying an ammonium salt comprising obtaining
the ammonium salt from a fermentation reaction; mixing the ammonium salt
with an alcohol to create a mixture; heating the mixture in the presence
of a catalyst; and subjecting the mixture to a pervaporation process
The invention also provides for a method for purifying esters of organic
acids comprising splitting or converting the salt into its cationic and
anionic part (i.e. acid and base, respectively); mixing the anionic part
(acid) with an alcohol to create a mixture; heating the mixture in the
presence of a catalyst to create an ester; dehydrating the now heated
mixture; and separating the ester from the now-dehydrated mixture.
BRIEF DESCRIPTION OF THE DRAWING
The present invention together with the above and other objects and
advantages may best be understood from the following detailed description
of the embodiment of the invention illustrated in the drawings, wherein:
FIG. 1 is a schematic diagram of an exemplary ester production and
purification process in accordance with the present invention; and
FIG. 2 is a schematic diagram of an exemplary ester purification process
utilizing a plurality of pervaporation units, in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
A very facile, and low-energy-requiring process to make volatile alcohol
esters from fermentation-derived ammonium carboxylates and other organic
acids has been developed. The process employs certain hydrophilic
pervaporation membranes that pass ammorda and water vapor without passing
any volatile alcohol, and at relatively low temperatures of less than
100.degree. C. This process removes ammonia from any of the thermally
cracked ammonium salts while minimizing any loss of volatile alcohol from
the reaction mixture to assure high yields and conversions. Aside from
ammonium-based carboxylates, the process generally is applicable for the
conversion of weak, volatile bases which have boiling points at or below
120.degree. C. Such material in this category include the ammonium and
amine salts and also the amides, such as the pyridines
The invented process eliminates the need for high heat applications in the
refining process of fermentation-derived organic acids, thereby minimizing
the occurrence of side reactions between fermentation liquor impurities
which would otherwise lead to unwanted by-products.
This pervap-assisted esterification process can be used for a wide range of
fermentation-derived carboxylates. The following examples disclosed infra
for ethyl esterification of lactic acid, ammonium lactate, ammonium
propionate and butyl esterification of butyric acid are meant to be
illustrative of the wide ranging utility of the invention, and are not to
be construed as limitations to the invented process.
A laboratory scale pervap/esterification system manufactured by Zenon
(Burlington, Ontario) and modified by the inventors was utilized. A
simplified schematic diagram of the system is designated as numeral 10 in
FIG. 1.
The invented process 10 consists generally of a liquid recirculation loop,
a flat-cell pervaporation purifier and a permeate collection point. At the
beginning of the process, a feed solution, 12, consisting of an aqueous
solution of an organic acid, such as ammonium lactate, is supplied from a
fermentation process stream. Typically, this stream is obtained by
concentration and partial purification of the lactate in the fermentation
broth by a separation process such as desalting electrodialysis or other
means, followed by further concentration by evaporation. In instances
where an organic acid is not supplied as an ammonium salt, the salt is
first converted to the acid prior its mixture with other reactants in this
process.
The feed solution 12 is combined with an alcohol feed stream 16 to create a
reactants mixture 17. A myriad of alcohols are applicable, including, but
not limited to, methanol, ethanol, propanol, isopropanol and butanol.
Generally, alcohols containing from one to four carbons are preferred.
Mole ratios of the alcohol to the carboxyl group will vary but generally
will range from approximately 1:1 to 6:1. The resulting mixture is then
directed to an esterification reactor 14. Alternatively, the alcohol and
the feed solution can be placed separately in the esterification reactor
with mixture of these two reactants occurring inside the reactor.
The alcohol reacts with the lactate in the esterification reactor 14 in the
presence of a homogeneous or heterogeneous catalyst. If a heterogeneous
catalyst is used, the reactor 14 will include a containment device, such
as a packed bed, for the catalyst. A first product stream of the
esterification reaction is directed via a product transport means, such as
a conduit 18, to a reaction product separator 20. If the product is a
liquid, the reaction product separator 20 will be a pervaporation unit. If
the product is a vapor, a vapor permeation unit will be used as the
reaction product separator 20. Depending on the carboxylic salt
esterified, a myriad of pervaporation membranes are applicable, as noted
below. Generally, the membranes are designed to remove water from the
reaction mixture so as to shift the reaction further to the right. In the
case of ammonium salts, the membrane would also be ammonia (ammonium
hydroxide) permeable so that both water and ammonia are selectively
removed from the product mix of the esterification process.
A low pressure means 22 such as a vacuum or sweeping gas is applied to the
permeate chamber 23 to facilitate removal of the permeating water and/or
ammonia via vaporization or fluid collection. (One means for creating a
vacuum is through the utilization of the pressure drop resulting from the
condensation of the permeating vapors.) Generally, vacuum pressures of
approximately 50 to 75 torr for industrial processes and 100 to 150 torr
for laboratory-scaled conversions provide good results. Preferably, the
reactor 14 is maintained as a closed system to avoid excessive
vaporization of the alcohol in the reaction mixture. The pressure in
reactor 14 is autogenous and is thus dependent on temperature and
composition and is generally lower than 200 psig.
A means for returning the retentate 24, such as a conduit, is employed to
return the retentate back to the esterification reactor 14 for additional
conversion. This additional conversion is facilitated in as much as
equilibrium constraints have been relieved by removing products of the
reversible reaction.
A second product stream of the esterification reaction, containing ester,
excessive alcohol and small amounts of water, impurities, and unconverted
lactate such as ammonium lactate, is directed via a second product stream
directing means 26 to a first distillation means 28, such as a thermal
column. The distillation means 28 removes alcohol from the second product
stream, with the alcohol redirected via a recirculation loop 30, aided by
a recirculation pump 31, to combine with the alcohol feed stream 16. The
higher fractions 29 resulting from this first distillation process,
including impurities and the desired ester, are directed to a second
distillation means 32 for further processing. Purified ester is obtained
here as distillate 33. Bottom fraction of this second distillation
process, consisting of unconverted lactate, impurities and by-products,
can be used as fuel or recycled for lactate recovery.
Reaction temperatures in the esterification reactor can range from
50.degree. C. to 200.degree. C., more typically from between 80.degree. C.
and 150.degree. C., and ideally from between approximately 75.degree. C.
and 120.degree. C. Lower temperatures, relative to those employed in
typical esterification procedures, are desired to avoid plasticization of
pervaporation membranes. Such temperatures are regulated by a temperature
regulating means 34, such as a thermostatically controlled heater, which
can be located just upstream of the esterification reactor 14, as shown,
or else integrally connected to the esterification reactor.
Another exemplary embodiment of the invention is depicted in FIG. 2 as
numeral 100 whereby a plurality of pervaporation membranes are utilized. A
feed solution 112 as a fermentation-derived, aqueous solution containing
the desired organic acid as a salt, such as ammonium lactate, is first
concentrated and partially purified as in the first embodiment. These
concentration and purification steps are not shown. In the case of
ammonium lactate, the feed solution 112 contains 60 to 80 percent
concentration of the lactate in water and small amounts of residual
carbohydrates, proteins, amino acids, mineral salts, etc. The feed
solution is initially placed into an esterification reactor 116.
An alcohol feed stream 114 is also fed into the esterification reactor 116.
Alternatively, and as is shown in FIG. 1, the alcohol feed stream 114 is
combined with the feed solution to create a mixture, which in turn is
placed into the esterification reactor 116.
With all reactants present in the reactor 116, reaction occurs in the
presence of a homogeneous or heterogenous catalyst. Catalyst types,
reaction temperatures, and pressures are similar to those disclosed in the
operation of the process 10 depicted in FIG. 1.
A first product stream 118, either of liquid- or vapor-phase, is directed
from the esterification reactor 116 to a first membrane separation unit
120, and subsequently to a second membrane separation unit 122. If the
first product stream 118 is a liquid, the membrane separation units 120,
122 are pervaporation units. If the first product stream 118 is a vapor,
then the membrane separation units 120, 122 are vapor permeation units.
The membrane separation units 120, 122 comprise two chambers separated by
a first membrane 121 and a second membrane 123 respectively. A first
upstream-side chamber 124, or feed/retentate chamber accommodates the
incoming first product stream 118, while a first permeate chamber 126 is
adapted to receive water, and in the case of ammonium carboxylate
processing (or other amine-salt processing), ammonia, amine salts such as
triethylammonium lactate, and volatile amines such as trimethylamine and
triethylamine. As such, the first membrane 121 possesses such selectivity
that it can effectively permeate water and ammonia and effectively retain
alcohol and ester. As noted infra, several commercially available
membranes, comprising a polyvinyl alcohol-based hydrophilic selective
layer, have shown such separation selectivity. A vacuum which is generated
either by condensation of the volatile permeate, or a sweeping gas (i.e.,
nitrogen, helium, argon, or any other inert gas) is applied to the
permeate chamber to facilitate removal of the permeated water and
nitrogen-containing permeates, with these permeates recycled for use in
the fermentation process.
A first retentate feed stream 128 is then directed to a second
feed/retentate chamber 130 in the second membrane separator 122 containing
the second membrane 123. The second membrane 123 possesses such
selectivity that results in the effective permeation of the product ester
while retaining the alcohol, lactate and water.
A vacuum, created by condensation of the vapor, or sweeping gas is applied
to the downstream side or second permeate chamber 132 to facilitate
removal of the permeated ester which is considered a final product stream
134. The remaining second retentate stream 136 is then directed back to
the esterification reactor 116 for further conversion, thereby further
facilitating reaction equilibrium shift to the right.
Catalyst and Membrane Detail
Many esterification or transesterifcation catalysts can be utilized in the
esterification units 14 and 116. These catalysts include sulfuric acid,
p-toluene sulfonic acid (p-TSA), 4-dimethyl aminopyridine (DMAP), stannous
octoate, lipases, esterases, the acidic resins such as those marketed
under the Amberlyst trade name, and long chain non-volatile amines such as
the C.sub.8 -C.sub.10 straight-chain tertiary amine mixture marketed as
Alamine 336 (Henkel Corp., Gulph Mills, Pa.), The DMAP and amine catalysts
are particularly applicable in ammonium carboxylate conversion processes.
One type of resin, marketed as Amberlyst 15.TM. and Amberlyst XN 1010.TM.
by Rohm and Haas Co., Philadelphia, Pa., consists of a bead form
macroreticular, strongly acidic resin, having a polymeric matrix of
sulfonated polystyrene that is cross-linked with divinylbenzene.
Water is selectively removed from the reaction mixture by its transport
through the pervaporation membrane contained in the pervaporation purifier
20. While the effective area of the pervaporation membrane used for the
following examples was from 62.5 to 182 square centimeters (cm.sup.2),
surface areas of the membrane can vary, depending on flow rates and
viscousness of the fermentation liquor. Generally, flux rates, measured in
kilograms per square meter per hour (kg/m.sup.2 /hr) of from 0.08 to 3 are
obtainable, with flux rates of 0.1 to 1 kg/m.sup.2 /hr preferred.
Generally, the pervaporation membrane employed consists of a nonporous
polyvinyl alcohol-active layer or a nonporous organophilic
polydimethylsiloxane-active layer on a porous supporting layer and
resistant to certain, desired products. Membranes with a polyvinyl
alcohol-based hydrophilic selective layer effectively permeate water and
ammonium while retaining alcohol and ester. For example, membranes
manufactured by GFT in Neunkirchen-Heinitz, Germany, as the GFT PerVap
1001 or 1005 names consist of a membrane with a non-porous
polyvinyl-alcohol active layer on a porous supporting layer made of
polyester and polyacrylonitrile, to provide resistance to organic acids.
An alkali-resistant membrane, marketed as GFT PerVap 2001 consists of a
non-porous polyvinylalcohol active layer on a porous supporting layer made
of polyacrylonitrile. Another applicable organic acid-resistant membrane
is marketed as TexSep 1B, and consists of a membrane with a non-porous
polyvinyl-alcohol (PVA) active layer on a porous supporting layer,
resistant to organic acids.
Generally, hydrophobic compounds can be used as the active layer of organic
permeable membranes. As such, membranes incorporating polydimethylsiloxane
in their organic permeable active layer, such as GFT Per Vap 1170.TM.
membrane from Neunkirchen-Heinitz, Germany, provide ester selectivity.
Other examples of hydrophobic compounds used as constituents of the active
layer include copolymers of styrene and styrene derivatives, polyether
block amides, and polytrimethylsilylpropyne.
EXAMPLE 1
Ethyl esterification of lactic acid was carried out by reacting ethanol
with lactic acid. The initial feed solution contained 55.4 weight percent
ethanol, 37.5 weight percent lactic acid and 6.7 weight percent water. The
molar ratio of ethanol to lactic acid was 2.8 in the feed. The lactic acid
used was a commercial food grade fermentation-derived lactic acid. Corn
steep liquor and maltose were added to the feed, each at 0.5 weight
percent of lactic acid, to simulate the impurities that are typically
present in the fermentation-derived lactic acid after primary
purification. Identical feed solutions were placed into the
pervap/esterification system and a simple flask reactor for parallel
esterification experiments. In both systems, the catalyst was Amberlyst 15
at 3 weight percent of lactic acid.
In the pervaporation assisted esterification process, the pervaporation
membrane was the GFT Pervap 1005. The membrane surface area was 62.5
cm.sup.2. The temperature of the reaction mixture was maintained at
80.degree. C., and the permeate side vacuum pressure was 4-25 millibar
(mbar). The reaction temperature in the simple flask reactor was
86.degree. C., which was the boiling temperature of the reaction mixture.
After 166 hours, the reaction was terminated in both systems.
The conversion in the pervaporation assisted esterification was found to be
90 percent, compared with the 75 percent conversion for the simple flask
esterification. The performance of the pervaporation separation was found
to be satisfactory. The membrane selectivity for water over ethanol was
700 and the average water flux was 0.18 kg/m.sup.2 /h, ranging from 0.49
kg/m.sup.2 /h at 9 percent water to 0.1 kg/m.sup.2 /h at 3.2 percent
water.
EXAMPLE 2
Ethyl esterification of lactate (in ammonium lactate) was conducted by
reacting ethanol with ammonium lactate. The initial reactant mixture 17
contained 36.6 weight percent ethanol, 42.5 weight percent ammonium
lactate and 20.9 weight percent water. The molar ratio of ethanol to
lactate in the feed was 2.0. The ammonium lactate solution was prepared
from neutralization of a commercial 88 percent lactic acid solution with
ammonium hydroxide.
Identical feed solutions were placed into the pervap/esterification system
and the control process as outlined supra, which was a simple flask
reactor. In both systems, the catalyst was 4-dimethylaminopyridine (DMAP)
at 1.0 weight percent of ammonium lactate. In the pervap-assisted
esterification, the pervaporation membrane was the GFT PerVap 2001.
Temperature of the reaction mixture was maintained at 95.degree. C.
Permeate side vacuum pressure was between 37 and 100+torr. Permeate was
collected by a combination of five cold traps and acid traps in series,
arranged as follows: cold trap #1 (dry ice-acetone mixture), 3.0M sulfuric
acid trap #1, 3.0M sulfuric acid trap #2, cold trap #2 (approximately
-45.degree. C.), and cold trap #3 (dry ice-acetone mixture). Acid traps
were changed during the experiment. The water flux decreased from 0.50
kg/m.sup.2 h to 0.12 kg/m.sup.2 /h during the experiment (based on the
mass of permeate collected by cold trap #1), indicating a decrease in
water content of the reaction mixture. The reaction temperature in the
simple flask reactor was 84.degree. to 85.degree. C., which was the
boiling temperature of the reaction mixture. After 104 hours, the reaction
was terminated in both systems. The membrane surface area was 182
cm.sup.2.
Reaction mixture samples were taken during the experiment and analyzed;
ethyl lactate and lactamide concentrations were measured by HPLC and
ammonium lactate concentrations were measured by an ammonium electrode.
The final concentrations in the reaction mixture from the pervap-assisted
esterification were 4.3 weight percent ethyl lactate and 4.7 weight
percent lactamide, compared to 2.4 weight percent and 1.5 weight percent
respectively from the simple flask reaction. Lactate conversion was 12.1
percent from the pervap assisted esterification, compared with 7.6 percent
from the simple flask reaction, showing an approximately 60 percent
increase due to the invented process.
Ammonium concentrations in the two acid traps were measured by ammonium
electrode and found to range from 884 ppm to 4,410 ppm. Cold trap #1
samples were analyzed by HPLC, and ethanol and ethyl lactate
concentrations were found to be below the detection limit.
EXAMPLE 3
Ethyl esterification of ammonium lactate was repeated without the use of
4-dimethylaminopyridine. The reactant mixture contained 36.6 weight
percent ethanol, 42.5 weight percent ammonium lactate and 20.9 weight
percent water. The molar ratio of ethanol to lactate was 2.0. Identical
reactant mixtures were placed into the pervap/esterification system and in
the control flask reactor. No esterification catalyst was used for either
system. In the pervap-assisted esterification, the pervaporation membrane
was the GFT PerVap 2001. The temperature of the reaction mixture was
maintained at 95.degree. C., and permeate vacuum pressures ranged from
between approximately 37 and 53 torr. The water flux was measured as 0.57
kg/m.sup.2 /h between elapsed times of 18 and 21 hours flux (based on the
mass of permeate collected by cold trap #1). The membrane surface area was
182 cm.sup.2.
Permeate was collected by a combination of five cold traps and acid traps
in the following series: cold trap #1 (dry ice-acetone mixture at -70
.degree. C. or 2.degree. C.), acid trap #1 , acid trap #2, cold trap #2
(approximately -45.degree. C.), and cold trap #3 (dry ice-acetone
mixture). 1.5M sulfuric acid was used (instead of 3.0M) in the acid traps.
Acid traps were changed during the experiment. The reaction temperature in
the simple flask reactor was 84.degree.-85.degree. C., which was the
boiling temperature of the reaction mixture. After 49 hours, the reaction
was terminated in both systems.
Reaction mixture samples were taken during the experiment and analyzed;
ethyl lactate and lactamide concentrations were measured by HPLC. Final
concentrations in the reaction mixture from the peryap-assisted
esterification were 5.5 weight percent ethyl lactate and 2.9 weight
percent lactamide, versus 3.0 weight percent and 1.2 weight percent
respectively for the control reactor. The estimated lactate conversion was
14.5 percent from the pervap assisted esterification, compared with 7.9
percent from the control reactor, showing an almost 84 percent increase
due to the invented process.
Ammonium concentrations in the two acid traps, as measured by ammonium
electrode, ranged from 436 ppm to 1,458 ppm.
EXAMPLE 4
Ethyl esterification of lactate (in ammonium lactate) was carried out by
reacting ethanol with ammonium lactate. The initial feed solution
contained 63.8 weight percent ethanol, 24.7 weight percent ammonium
lactate, and 11.5 weight percent water. The molar ratio of ethanol to
lactate in the feed was 6.1. The ammonium lactate solution was prepared
from neutralization of a commercial 88 percent lactic acid solution with
ammonium hydroxide solution.
Identical reactant mixtures were placed into the pervap/esterification
system and the flask reactor control. In both systems the catalyst was
4-dimethylaminopyridine (DMAP) at 10 weight percent of ammonium lactate.
In the peryap-assisted esterification, the pervaporation membrane was the
GFT PerVap 2001. Membrane surface area was 182 cm.sup.2. Temperature of
the reaction mixture was maintained at 95.degree. C. Permeate-side vacuum
pressure ranged from between approximately 53 and 73 torr. Permeate was
collected by a combination of four cold traps and acid traps in series,
arranged in the following order: cold trap #1 (dry ice-acetone mixture or
2.degree. C.), 1.5M sulfuric acid trap #1, 1.5M sulfuric acid trap #2, and
cold trap #2 (approximately -45.degree. C.). Acid traps were changed
during the experiment. The permeate flux (based on the mass of permeate
collected by cold trap #1) was measured as 0.36 kg/m.sup.2 /h between
elapsed times of 14 and 18 hours. The reaction temperature in the simple
flask reactor control was 81.degree. to 82.degree. C., which was the
boiling temperature of the reaction mixture. After 71 hours, the reaction
was terminated in both system and the products were analyzed.
Concentrations of unreacted ammonium lactate, calculated by the ammonium
concentrations measured by ammonium electrode were 18.9 weight percent in
the peryap-assisted esterification process and 22.8 weight percent in the
control process. Concentrations of ethyl lactate, as measured by HPLC, in
the pervap-assisted process was 2.9 weight percent versus a 1.1 weight
percent yield in the control flask. The estimated lactate conversion was
14.5 percent in the pervap-assisted esterification, compared to 7.2
percent in the control process, showing an approximately 100 percent
increase attributable to the invented process.
EXAMPLE 5
Ethyl esterification of propionate (in ammonium propionate) was conducted
by reacting ethanol with ammonium propionate. The reactant mixture
contained 67.7 weight percent ethanol, 22.3 weight percent ammonium
propionate and 9.9 weight percent water. The molar ratio of ethanol to
propionate in the reactant mixture was 6.0. The ammonium propionate
solution was prepared from neutralization of a commercial 100 percent
propionic acid solution with ammonium hydroxide solution. Identical
reactant mixtures were placed into the pervap/esterification system and
the control flask configuration. Both systems utilized the esterification
catalyst 4-dimethylaminopyridine (DMAP) at 5 weight percent of ammonium
propionate. The pervaporation membrane used was the GFT PerVap 2001, and
had a surface area of 182 cm.sup.2. Temperature of the reaction mixture
was maintained at 95.degree. C., and permeate side vacuum pressure was
between 48 and 70 torr. The permeate was collected by 5 cold traps and
acid traps arranged in the following order: cold trap #1 (either dry
ice-acetone mixture or 2.degree. C.), 1.5M sulfuric acid trap #1, 1.5M
sulfuric acid trap #2, cold trap #2 (approximately -45.degree. C.), and
cold trap #3 (dry ice-acetone mixture). Permeate flux was measured as 0.48
kg/m.sup.2 /h between elapsed times of 3 and 6 hours (based on the mass of
permeate collected by cold trap #1). The reaction temperature in the
simple flask reactor was 81.degree. C., which was the boiling temperature
of the reaction mixture. The reaction was terminated in both systems after
76 hours.
Analysis of the permeate revealed concentrations of 8.8 weight percent
ethyl propionate, compared to 1.9 weight percent in the control process.
Propionate conversion was estimated at 40.7 percent in the peryap-assisted
esterification, compared to 4.7 weight percent in the control process, or
an approximate 760 percent increase attributable to the invented process.
EXAMPLE 6
Ethyl esterification of lactic acid was carried out by reacting ethanol
with lactic acid. The initial reactant mixture contained 41 weight percent
ethanol, 32.1 weight percent lactic acid, and 26.9 weight percent water.
The mole ratio of ethanol to lactate in the feed was 2.0.
The lactic acid used was a commercial lactic acid. Corn steep liquor and
maitose were each added at 0.5 weight percent to simulate the impurities
typically present in fermentation broth after primary purification. The
esterification catalyst was para-toluene sulfonic acid (pTSA) added at 1
weight percent of lactic acid. The pervaporation membrane was GFT PerVap
1005, and had a surface area of 182 cm.sup.2. Temperature of the reaction
mixture was maintained at 80.degree. C., and the permeate-side vacuum
pressure was approximately 3 millibar. (1 millibar=0.75 torr). The
reaction was terminated after 8 hours.
Final reaction product contained 20.5 weight percent ethyl lactate, 32.9
weight percent ethanol, 27.7 weight percent water and 18.9 weight percent
lactic acid. The average water flux was 1.15 kg/m.sup.2 /h. The permeate
contained greater than 98 weight percent water and less than 2 weight
percent ethanol.
EXAMPLE 7
Ethyl esterification of lactic acid was carried out by reacting ethanol
with lactic acid. The reaction system had a larger flat-cell pervaporation
module (effective area of 182 cm.sup.2) and the sizes of other components
were upgraded. Initial feed solution contained 47.4 weight percent
ethanol, 46.3 weight percent lactic acid and 6.3 weight percent of water.
Molar ratio of ethanol to lactic acid was 2.0 in the feed. The lactic acid
used was a commercial food grade fermentation-derived lactic acid. Corn
steep liquor and maltose were added to the feed, each at 0.5 weight
percent of lactic acid, to simulate the impurities that are typically
present in the fermentation-derived lactic acid after primary
purification. Amberlyst XN-1010 was used at the catalyst at 10 weight
percent of lactic acid. The pervaporation membrane was the GFT PerVap
1005. Temperature of the reaction mixture was maintained at 95.degree. C.,
and the permeate-side vacuum pressure was less than 0.5 mbar. After 81.7
hours, the reaction was stopped.
Final reaction product consisted of 76.3 weight percent ethyl lactate, 23.2
weight percent ethanol, and 0.5 weight percent lactic acid. Water
concentration was below detection limits. Average water flux was 0.41
kg/m.sup.2 /hr, and ranging from 1-3 kg/m.sup.2 /hr at greater than 7
weight percent water to less than 0.1 kg/m.sup.2 /hr at low water
concentrations (for example below 0.4 weight percent).
Conversion in this pervap-assisted esterification process was greater than
99 percent.
EXAMPLE 8
This example is based on the process depicted in FIG. 2 whereby organic
compound-permeable pervaporation membranes are utilized, instead of
distillation, to separate ester from final product liquors.
One thousand, five hundred (1,500) grams of a feed, simulating an
esterification reaction mixture containing 21 weight percent lactic acid,
34.4 weight percent ethanol, 31 weight percent ethyl lactate, and 13.6
percent water, was fed to the pervap-assisted esterification system. The
GFT PerVap 1170 was the pervaporation membrane used, with an effective
area of 62.5 cm.sup.2.
The mixture was subjected to pervaporation at 80.degree. C. The
permeate-side vacuum pressure was approximately 8 mbar. The permeate was
condensed and collected in a cold trap. After 20.4 hours, separation of
the ester by pervaporation was terminated with a final retentate
composition of 22.6 weight percent lactic acid, 34.9 weight percent
ethanol, 13.6 weight percent water and 29 weight percent ethyl lactate.
The permeate samples were found to contain 91.3-91.9 weight percent ethyl
lactate, 4.5 to 4.8 weight percent ethanol, 1.6-2.3 weight percent lactic
acid and 1.6-1.8 weight percent water.
Ethyl lactate was selectively removed from the reaction mixture to the
permeate by using pervaporation. The ethyl lactate flux was 0.08-0.09
kg/m.sup.2 /h.
EXAMPLE 9
Butyl esterification of butyric acid was carried out by reacting butanol
with butyric acid. The initial feed solution contained 63.2 weight percent
butanol, 30.3 weight percent butyric acid, and 6.2 weight percent water.
The molar ratio of butanol to butyric acid in the feed was 2.5. The
butyric acid used was a commercial reagent-grade butyric acid. Corn steep
liquor and maltose were added to the feed, each at 0.5 weight percent of
butyric acid, to simulate the impurities that are expected to be present
in the fermentation-derived butyric acid after primary purification. The
same feed solution was placed into the pervap/esterification system and
the simple flask reactor for parallel esterification experiments. In both
systems, the catalyst was Amberlyst 15 at 5 weight percent of butyric
acid. In the pervap-assisted esterification, the pervaporation membrane
was the TexSep 1B, with a surface area of 62.5 cm.sup.2.
The temperature of the reaction mixture was maintained at 80.degree. C.,
and the permeate side vacuum pressure was 3-17 mbar. The reaction
temperature in the simple flask reactor was 93.degree. C., which was the
boiling temperature of the reaction mixture. After 95 hours, the reaction
was terminated in both systems. The conversion in the pervap-assisted
esterification was found to be 93 percent, compared with the 75 percent
conversion for the simple flask esterification.
Membrane selectivity for water over butanol was greater than 6000 and the
average water flux was 0.36 kg/m.sup.2 /h, ranging from 1.04 kg/m.sup.2 /h
at 6 percent water to 0.12 kg/m.sup.2 /h at 1.1 percent water. The
invention also provides a method for esterifying a salt of a fermentation
derived carboxylic acid comprising splitting the salt into its cationic
and anionic part; mixing the anionic part with an alcohol to create a
mixture; heating the mixture in the presence of a catalyst to create an
ester; dehydrating the now heated mixture; and separating the ester from
the now-dehydrated mixture. The step of splitting the salt into its
cationic and anionic parts consists of subjecting the salt to mineral
acid. The mineral acid is present in equimolar quantities to the anionic
part. The organic acid is selected from the group consisting of lactic
acid, butyric acid, succinic acid, acetic acid, propionic acid and
combinations thereof. The alcohol is selected from the group consisting of
methanol, ethanol, propanol, isopropanol, butanol and combinations
thereof. The alcohol is mixed with the anionic part in a molar ratio
selected from between 1:1 to 6:1. The mixture is heated to a temperature
selected from a range of between approximately 75.degree. C. to
150.degree. C. The step of dehydrating the mixture consists of contacting
the mixture to a pervaporation membrane selective to water so as to remove
water from the mixture. The step of removing the ester from the
now-dehydrated mixture consists of distilling the ester from the mixture.
Alternatively, the step of removing ester from the now-dehydrated mixture
consists of subjecting the now-dehydrated mixture to a pervaporation
membrane selective to ester.
While the invention has been described with reference to details of the
illustrated embodiment, these details are not intended to limit the scope
of the invention as defined in the appended claims,
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